These pipes belong for example to a water delivery network. In their most common form these pipes are constituted by an end to end assembly of segments of pipe made from pre-stressed concrete and having a relatively large diameter of typically 0.5 m to more than 6 m. Water flows through said pipes under a pressure of up to around twenty bars. These segments of concrete pipe can incorporate an interior metal cylinder (liner). The latter is not designed, however, to carry the stress in terms of pressure due to the fluid flowing through. This stress is carried by passive reinforcement (pre-fabricated cylindrical reinforcement cage) or by the pre-stressing of the concrete. The latter is realized by means of wires wound in a spiral outside of the concrete core of the pipe segment. During manufacture of this segment its concrete core is rotated about its axis to receive the wire which is checked in order to be brought under pressure. This wire is then protected against corrosion by projecting a supplementary layer of concrete or mortar over twenty to thirty millimeters.
The wall of the pipe usually comprises:                a concrete core incorporating a watertight liner constituted by a ductile cylinder made from thin steel (so-called embedded-cylinder pipe). The concrete of the core is distributed between an internal layer of a few centimeters in thickness which is situated on the internal side of the pipe and a thicker external layer which in most cases is not reinforced;        pre-stressing wires wound in one or two layers around the concrete core;        protective anti-corrosion mortar surrounding the wires in order to passivate them;        an optional paint or resin improving the anti-corrosion protection.        
Pipes of this type are most frequently embedded. They are exposed to a risk of corrosion according to the aggressiveness of the environment. The most common form of degradation occurs as follows:                migration of aggressive ions across the protective mortar;        corrosion of the pre-stressing wires;        breaking of the pre-stressing wires and local delamination;        general delamination of the external mortar;        depassivation of the wires and acceleration of corrosion.        
The process can then accelerate and lead to the breaking of the pipe. Methods of magnetic or acoustic detection allow breaks in wire to be located and the state of the pipe to be assessed. Depending upon the assessed state a decision to repair can be taken.
Repair is generally carried out from the exterior. New reinforcements, passive or pre-stressed, are placed around the pipe in order to collar it. See for example international patent application published as WO 03/014614.
Repairs can also be carried out from the inside by incorporating within the pipe a resistant core for the purpose of re-establishing the resistance lost through the breaking of the pre-stressing wires. Repairs carried out from the inside are generally more expensive. Such repairs are carried out when the excavation works are impossible or difficult.
Repairs from the inside generally consist in placing a metal liner within the pipe. The interstice between the new resistant liner and the pipe is filled with grout. One difficulty is that a local error in realization can lead to infiltrations of water in the injected interstice. This water penetration can cause the concrete core of the pipe to be brought under pressure and can make the new resistant liner inefficient. This will result in a risk of a break in the pipe outside of the new liner.
Another difficulty is that the new metal liner must be welded in situ, both longitudinally and transversally. Such welds are difficult to perform and control and may fail, leading to a bursting of the repaired pipe.
When repairing from the inside the reinforcements added cannot be pre-stressed. When the pipe is brought under pressure these reinforcements undergo a certain elastic deformation (increase in their diameter) which causes cracking of the concrete of the core of the pipe. The concrete breaks in traction for a very small deformation, no material having the capacity to carry any significant stress for such extension. The cracking of the concrete causes two disadvantages. It worsens the flexural strength of the pipe and hence its capacity to resist dissymmetrical thrusts of the earth. It also allows corrosion to progress from the outside environment to the inside of the pipe. It also allows corrosion to progress from the exterior to the interior of the pipe. This risks causing early corrosion of the new reinforcement if it is metal. This problem often leads to the solutions for repairs from the inside with a basis of metal liners to be dismissed.
An alternative solution is disclosed in US 2005/0246995 A1 where a composite structural reinforcement is applied, through in situ stratification of at least one band of reinforcement fibers and a resin matrix, the band being arranged according to a substantially helical path along the internal side of the pipe.
When the pipe is brought back into service the pressure of the liquid tightens the fibers of the band which, if it has appropriate dimensions, will be able to carry most of the radial stress. The composite structure avoids the risks of corrosion encountered with solutions using metal liners. The helical layout allows the in situ stratification of the composite to be carried out which facilitates implementation and avoids the problems of watertight connection, the band covering itself with each turn.
Although this method of reinforcing an embedded cylinder pipe is very efficient, it has been noticed that the application of the band of reinforcement fibers may be difficult and time consuming when using standard methods such as manual application of said band.
One has noticed for example that the band may locally detach or be crumpled when operating conditions are not satisfactory.